My experience is that the inletting on McMillans are more precise, the stock has far less flex in the forearm, and it typically has a higher strength-to-weight ratio (subjective, I know). You can get it in virtually every possible configuration (and every color combination). The B&C is a $150-200 stock, and the McMillan is a $450-500 stock.
McMillan will also take your rifle and bed your stock to the gun. At this they do a jam-up job. B&C and HS, in my experience, will tell you that bedding is unnecessary and even voids the warranty (in the case of HS).
Again though, I have to stress...the B&C on this EW is a darn good factory stock. I have Weatherbys and a Sako that came with absolute crap for stocks; at least Winchester is trying.
Comparing flex in the forearm would require some measurable means to apply the pressure and a dial indicator to measure the movement. Seat of the pants testing is not reliable beyond...it flexes a lot vs it does not flex a lot.
Precise inletting may be true, I have not looked at MCM's closely but in my opinion. I want precise inletting on my blued and walnut guns, I want a gap on my synthetic stocked rifles. The barrel was not centered in the channel on my 300WSM but it was after I bedded it, so no issues.
I would not send my rifle anywhere to have it bedded, number one, it adds to the cost and number two, I can bed my rifles just fine and everyone with any interest in accurate rifles should learn to do it (not that you don't).
Strength to weight ratio *may* be true but again, show me the tests. There is a limit to how strong a stock needs to be, I don't think anyone is going to use a MCM as a substitute for a shovel, pry bar or sledge hammer.
Face it, the attraction of the MCM is simply the weight followed by the option for the crazy ass colors.
There is a break point when cost exceeds true value and everything beyone is simply fluff.
Put it another way, would the MCM fans pay a 1000.00 for a 12 ounce stock? How about 1500.00 for an 8 ounces stock? 
